Hybridization at the nanometer scale organic and inorganic compounds is an important and evolutionary way to create new materials. Organic-inorganic polymer hybrids, wherein organic polymers are dispersed in inorganic solids on a nano or molecular level, have raised a great deal of scientific, technological and industrial interests because of their unique properties.
To elaborate organic-inorganic polymer hybrids, a sol-gel process using metal alkoxides is the most useful and important approach. By properly controlling the reaction conditions of hydrolysis and polycondensation of metal alkoxydes, in particular of alkoxysilanes (e.g. tetramethoxysilane (TMOS) or tetraethoxysilane (TEOS)), in the presence of pre-formed organic polymers, it is possible to obtain hybrids with improved properties compared to the original compounds. The polymer can enhance the toughness and processability of otherwise brittle inorganic materials, wherein the inorganic network can enhance scratch resistance, mechanical properties, and surface characteristics of said hybrid.
Hybrids made from sol-gel technique starting from fluoropolymers, in particular from vinylidene fluoride polymers are known in the art.
Thus, paper OGOSHI, Tomoki, et al. Synthesis of Poly(vinylidene fluoride) (PVDF)/Silica Hybrods having interpenetrating polymer network structure by using crystallization between PVDF chains. (A) J. polym. sci., A, Polym. chem. 2005, vol. 43, p. 3543-3550. discloses the synthesis of certain PVDF/silica hybrids by reacting a solution in DMF and gamma-butirolactone of PVDF with TMOS in the presence of a catalytic amount of HCl.
Nevertheless, despite the in situ formation of the inorganic domains which should provide for high dispersion-ability, it happens that these interface among organic phase and inorganic phase represent disrupting surfaces which might behave as weakness points depleting advantages in mechanical properties, and/or might cause inorganic domain to ‘coagulate’ to a large extent depleting the homogeneity advantages, e.g. in adhesion and/or other surface properties.
Attempts have been made in the art for ensuring chemical bonding among certain organic polymers and certain inorganic domains dispersed therein, via techniques differing from the sol/gel above mentioned.
Thus, U.S. Pat. No. 6,620,516 (ASAHI KASEI KK) 16, Sep. 2003 discloses an organic domain/inorganic domain hybrid material wherein the organic domain comprises a water-soluble or water-dispersible organic polymer having a plurality of carboxylic acid groups, and the organic domain and the inorganic domain being ionically bonded to each other through the carboxylic groups of the organic polymer to form an ionically crosslinked structure. These hybrids are manufactured by reaction between the organic polymer as above detailed and certain metasilicate anions in an aqueous medium under basic conditions in the presence of certain divalent metal cations which will ensure the formation of the ionic network through simultaneous ionic chemical bond to the carboxylate and silicate groups.
Similarly, U.S. Pat. No. 7,244,797 (ASAHI KASEI KK) 17, Jul. 2007 discloses a similar approach, wherein, in addition, the organic polymer can comprise cationic functionalities (e.g. quaternary ammonium groups) which are ionically bound to the metasilicate function of the inorganic domain.
Nevertheless, these approaches have not been proposed as suitable for fluoropolymers.
SOUZY, Renaud, et al. Functional Fluoropolymers for fuel cell membranes. Prog. Polym. Sci. 2005, vol. 30, p. 644-687. discloses in its section 3.3.2 composite membrane notably made by formation of an interpenetrating network of the organic and inorganic fractions. As an example, sol-gel acid-catalyzed hydrolysis/polymerization of tetraethoxysilane (TEOS) on NAFION® pre-formed fluoroionomer membrane is mentioned as yielding a Nafion®-silica hybrid membrane.
EP 1389634 A (DAIKIN INDUSTRIES LTD) 18, Feb. 2004 discloses a surface-treatment agent comprising:                a) a hydrolyzable metal alkoxyde, which can be notably TEOS;        b) a fluorocompound comprising a perfluoroalkyl group and a functional group reactive towards the above mentioned metal hydrolyzable compound; and        c) an adhesion improvement agent.        
In preferred embodiments, compound b) is a perfluoropolyether comprising functional groups of formula:
wherein Y is H or lower alkyl group; m and n is from 0 to 2; R1 is a hydrolysable group or a chlorine atom; R2 is a hydrogen atom or a inert monovalent group, M is a metal or a reactive group selected from the group consisting of an isocyanate group, a carboxyl group, a hydroxyl group, a glycidyl group, a phosphate group, an amino group, and a sulfonate group.
There is thus still a shortfall in the art for fluoropolymer-based hybrid organic/inorganic composites wherein organic phases and inorganic phases are chemically bound each other through covalent bounds, which could override drawbacks of hybrids of the prior art.